1. Field of the Invention
The present invention relates to a method and apparatus for detecting objects with time domain impulsive signals, and it more specifically relates to an apparatus and method for detecting visually obscured objects with ultra wide band (UWB) RF signals.
2. Description of the Related Art
UWB technology has been around for several decades, and it has been used for radar-based applications in the past. Developments in high-speed switching technology are making UWB technology more attractive for low-cost consumer communications applications. Many companies are currently working on RandD projects that explore the possibility of extending UWB technology into the high-rate communications arena, and the FCC is setting emissions limits that would permit deployment of UWB communications systems on an unlicensed basis.
An UWB radio is an RF communications device that uses high-bandwidth microwave pulses for transmitting digital data over a wide spectrum of frequency bands using very low power intensity. These devices can transmit data at very high rates (for wireless local area network applications) and very low rates (for telemetry applications). Within the power limit allowed under the current FCC regulations, UWB radios can carry large amounts of data over a short distance, at very low power. An UWB radio has the ability to carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and at higher power levels. If higher power levels are used, UWB signals can travel significantly greater ranges.
UWB radio broadcasts use digital pulses timed very precisely. UWB radios do not use sine waves. The transmitter and receiver are highly synchronized, and they send and receive pulses with an accuracy of trillionths of a second. UWB technology is used in very high-resolution radars and precision (sub-centimeter) radio location systems.
Since UWB transmissions are high speed pulses instead of sine waves, UWB transmissions have a high degree of immunity to multipath fading. The constructive and destructive interference created by multiple reflections of the same sine wave signal being received simultaneously is known as multipath fading. This immunity to multipath fading makes UWB technology well suited for applications in environments that would otherwise suffer from multipath fading associated with sine wave transmissions.
UWB devices use the same increasingly crowded radio frequencies that many other systems use. UWB devices typically send out short electromagnetic pulses of half a billionth of a second, and the pulses are followed by pauses that of approximately 200 times that length. By spreading the pulses over a wide area of the spectrum (roughly 1 GHz), UWB devices use extremely low power and wide total bandwidths. UWB technology proponents envision applications such as home security and personal-area networks that activate home appliances. Police and fire departments are currently testing UWB devices that can detect people behind walls.
The government and private industry have an increasing interest in UWB technology. Two main UWB applications of interest are the transmission of large volumes of voice and data at very high speeds with relatively little power, and wall penetrating radars that provide detailed Images of objects behind the wall. Precision locating systems are of interest to military, law enforcement, and rescue agencies. The FCC has approved limited productions of UWB radars for police and rescue workers.
The above described wall penetrating UWB systems may provide a view or image of what is behind a wall or visual impediment, but such systems cannot provide a rapid and certain determination of whether the objects are potentially dangerous objects of interest. Moreover, if the system provides a visual image of what is behind the wall, there is a possibility that the operator of the device may misinterpret the image. Accordingly, there is a need for an UWB detection system that can provide a rapid and certain determination of potentially dangerous objects of interest behind a visual impediment.
The present invention provides an UWB detection system and method that can provide a rapid and certain determination of potentially dangerous objects of interest behind walls or visual impediments. Ultra wide band RF impulsive signals are used to probe a target area. The return signals from the target area are received and processed. The processing of the return signals includes decomposing the return signals into time slice feature data. A known object of interest whose preexisting profile has been stored in a database is designated. The probability of detection of a known object of interest is based upon the magnitude of a vector that represents the distance between the time slice feature data and the coordinates of the known object of interest having a preexisting profile. When the magnitude of the vector is less than a predetermined amount, the existence of the known object is displayed to a user of the system.